Adaptation of control signaling transmissions to variations in respective resources

ABSTRACT

A method and an apparatus for a User Equipment (UE) to receive a first type of a Physical Downlink Control CHannel (PDCCH) or a second type of a PDCCH in a Transmission Time Interval (TTI) are provided whereby the first type of PDCCH and the second type of PDCCH convey respective Downlink Control Information (DCI) formats containing Cyclic Redundancy Check (CRC) bits scrambled with a Radio Network Temporary Identifier (RNTI). The method includes receiving by the UE a first bitmap associated with a number of TTIs equal to the first bitmap size, wherein each element of the first bitmap indicates whether a TTI is of a first type or of a second type, decoding by the UE only PDCCH of the first type if the TTI is of the first type, and decoding by the UE only PDCCH of the second type if the TTI is of the second type.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Applications No. 61/603,903 which was filed in the UnitedStates Patent and Trademark Office on Feb. 27, 2012, and No. 61/704,791which was filed in the United States Patent and Trademark Office on Sep.24, 2012, the entire disclosure of each of which is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to wireless communicationsystems. More particularly, the present invention is related to thetransmission and reception of physical downlink control channels.

2. Description of the Art

A communication system includes a DownLink (DL) that conveystransmission signals from transmission points such as Base Stations (BSor NodeBs) to User Equipments (UEs) and an UpLink (UL) that conveystransmission signals from UEs to reception points such as NodeBs. A UE,also commonly referred to as a terminal or a mobile station, may befixed or mobile and may be a cellular phone, a personal computer device,etc. A NodeB is generally a fixed station and may also be referred to asan access point or some other equivalent terminology.

DL signals consist of data signals carrying the information content,control signals carrying DL Control Information (DCI), and ReferenceSignal (RS) which are also known as pilot signals. A NodeB transmitsdata information or DCI to UEs through respective Physical DL SharedCHannels (PDSCHs) or Physical DL Control CHannels (PDCCHs).

UL signals also consist of data signals, control signals and RS. A UEtransmits data information or UL Control Information (UCI) to a NodeBthrough a respective Physical Uplink Shared CHannel (PUSCH) or aPhysical Uplink Control CHannel (PUCCH).

A PDSCH transmission to a UE or a PUSCH transmission from a UE may be inresponse to dynamic scheduling or to Semi-Persistent Scheduling (SPS).With dynamic scheduling, a NodeB conveys to a UE a DCI format through arespective PDCCH. With SPS, a PDSCH or a PUSCH transmission isconfigured to a UE by a NodeB through higher layer signaling, such asRadio Resource Control (RRC) signaling, and occurs at predetermined timeinstances and with predetermined parameters as informed by the higherlayer signaling.

A NodeB also transmits one or more of multiple types of RS including aUE-Common RS (CRS), a Channel State Information RS (CSI-RS), and aDeModulation RS (DMRS). The CRS is transmitted over substantially theentire DL system BandWidth (BW) and can be used by all UEs to demodulatedata or control signals or to perform measurements. A UE can determine anumber of NodeB antenna ports from which a CRS is transmitted through abroadcast channel transmitted from the NodeB. To reduce the overheadassociated with the CRS, a NodeB may transmit a CSI-RS with a smallerdensity in the time and/or frequency domain than the CRS for UEs toperform measurements. A UE can determine the CSI-RS transmissionparameters through higher layer signaling from the NodeB. DMRS istransmitted only in the BW of a respective PDSCH and a UE can use theDMRS to demodulate the information in the PDSCH.

FIG. 1 is a diagram illustrating a structure for a DL Transmission TimeInterval (TTI) according to the related art.

Referring to FIG. 1, a DL TTI 100 consists of one subframe 110 whichincludes two slots 120 and a total of NL_(symb) ^(DL) symbols fortransmitting of data information, DCI, or RS. The first M_(symb) ^(DL)subframe symbols are used to transmit PDCCHs and other control channels(not shown) 130. The remaining N_(symb) ^(DL)-M_(symb) ^(DL) subframesymbols are primarily used to transmit PDSCHs 140. The transmission BWconsists of frequency resource units referred to as Resource Blocks(RBs). Each RB consists of N_(sc) ^(RB) sub-carriers, or ResourceElements (REs), and a UE is allocated M_(PDSCH) RBs for a total ofM_(sc) ^(PDSCH)=M_(PDSCH)·N_(sc) ^(RB) REs for the PDSCH transmissionBW. Some REs in some symbols contain CRS 150, CSI-RS or DMRS. A unit ofone RB in the frequency domain and one subframe in the time domain isreferred to as a Physical Resource Block (PRB).

DCI can serve several purposes. A DCI format in a respective PDCCH mayschedule a PDSCH or a PUSCH transmission conveying data information toor from a UE, respectively. Another DCI format in a respective PDCCH mayschedule a PDSCH providing System Information (SI) to a group of UEs fornetwork configuration parameters, or a response to a Random Access (RA)by UEs, or paging information, and so on. Another DCI format may provideto a group of UEs Transmission Power Control (TPC) commands fortransmissions of respective PUSCHs or PUCCHs.

A DCI format includes Cyclic Redundancy Check (CRC) bits in order for aUE to confirm a correct detection. The DCI format type is identified bya Radio Network Temporary Identifier (RNTI) that scrambles the CRC bits.For a DCI format scheduling a PDSCH or a PUSCH to a single UE, the RNTIis a Cell RNTI (C-RNTI). For a DCI format scheduling a PDSCH conveyingSI to a group of UEs, the RNTI is a SI-RNTI. For a DCI format schedulinga PDSCH providing a response to a RA from a group of UEs, the RNTI is aRA-RNTI. For a DCI format scheduling a PDSCH paging a group of UEs, theRNTI is a P-RNTI. For a DCI format providing TPC commands to a group ofUEs, the RNTI is a TPC-RNTI. Each RNTI type is configured to a UEthrough higher layer signaling (and the C-RNTI is unique for each UE).

FIG. 2 is a block diagram illustrating an encoding process for a DCIformat according to the related art.

Referring to FIG. 2, in the decoding process 200, the RNTI of the DCIformat masks the CRC of the codeword in order to enable a UE to identifythe DCI format type. The CRC 220 of the (non-coded) DCI format bits 210is computed and it is subsequently masked 230 using the eXclusive OR(XOR) operation between CRC and RNTI bits 240. It is XOR(0, 0)=0, XOR(0,1)=1, XOR(1, 0)=1, XOR(1, 1)=0. The masked CRC is then appended to theDCI format bits 250, channel coding is performed 260, for example usinga convolutional code, followed by rate matching 270 to the allocatedresources, and finally by interleaving and modulation 280, and thentransmission of the control signal 290. For example, both the CRC andthe RNTI consist of 16 bits.

FIG. 3 is a block diagram illustrating a decoding process for a DCIformat according to the related art.

Referring to FIG. 3, in the decoding process 300, a received controlsignal 310 is demodulated and the resulting bits are de-interleaved 320,the rate matching applied at the NodeB transmitter is restored 330, anddata is subsequently decoded 340. After decoding, DCI format bits 360are obtained after extracting CRC bits 350 which are then de-masked 370by applying the XOR operation with the RNTI 380. Finally, the UEperforms a CRC test 390. If the CRC test passes, the UE considers theDCI format as valid and determines parameters for a PDSCH reception or aPUSCH transmission. If the CRC test does not pass, the UE disregards thepresumed DCI format.

A NodeB separately encodes and transmits a DCI format in a respectivePDCCH. To avoid a PDCCH transmission to a UE blocking a PDCCHtransmission to another UE, the location of each PDCCH transmission inthe time-frequency domain of the DL control region is not unique and, asa consequence, a UE needs to perform multiple decoding operations todetermine whether there is a PDCCH intended for it. The REs carryingeach PDCCH are grouped into Control Channel Elements (CCEs) in thelogical domain. For a given number of DCI format bits, the number ofCCEs for the respective PDCCH depends on the channel coding rate(Quadrature Phase Shift Keying (QPSK) is assumed as the modulationscheme). A NodeB may use a lower channel coding rate (more CCEs) forPDCCH transmissions to UEs experiencing low DL Signal-to-Interferenceand Noise Ratio (SINR) than to UEs experiencing a high DL SINR. The CCEaggregation levels can consist, for example, of 1, 2, 4, and 8 CCEs.

FIG. 4 is a diagram illustrating a transmission process of DCI formatsin respective PDCCHs according to the related art.

Referring to FIG. 4, in the transmission process 400, the encoded DCIformat bits are mapped to PDCCH CCEs in the logical domain. The first 4CCEs (L=4), CCE1 401, CCE2 402, CCE3 403, and CCE4 404 are used totransmit a PDCCH to UE 1. The next 2 CCEs (L=2), CCE5 411 and CCE6 212,are used to transmit a PDCCH to UE2. The next 2 CCEs (L=2), CCE7 421 andCCE8 422, are used to transmit a PDCCH to UE3. Finally, the last CCE(L=1), CCE9 431, is used to transmit a PDCCH to UE4. The DCI format bitsmay be scrambled 440 by a binary scrambling code and are subsequentlymodulated 450. Each CCE is further divided into Resource Element Groups(REGs) (i.e., “mini CCEs”). For example, a CCE consisting of 36 REs canbe divided into 9 REGs, each consisting of 4 Res. Interleaving 460 isapplied among REGs (blocks of 4 QPSK symbols). For example, a blockinterleaver may be used. The resulting series of QPSK symbols may beshifted by J symbols 470, and finally each QPSK symbol is mapped to anRE 480 in the control region of the DL subframe. Therefore, in additionto the CRS, 491 and 492, and other control channels (e.g., 493), the REsin the PDCCH contain QPSK symbols corresponding to DCI format for UE1494, UE2 495, UE3 496, and UE4 497.

For the PDCCH decoding process, a UE may determine a search space forcandidate PDCCH locations after it restores the CCEs in the logicaldomain according to a UE-common set of CCEs (Common Search Space or CSS)and according to a UE-dedicated set of CCEs (UE-Dedicated Search Spaceor UE-DSS). The CSS may consist of the first CCEs in the logical domain.PDCCHs for DCI formats associated with UE-common control information anduse SI-RNTI, or P-RNTI, or RA-RNTI, or TPC-RNTI, and so on, to scramblethe respective CRCs are always transmitted in the CSS. The UE-DSSconsists of CCEs used to transmit PDCCHs for DCI formats associated withUE-specific control information and use respective C-RNTIs to scramblethe respective CRCs. The CCEs of a UE-DSS may be determined according toa pseudo-random function having as inputs UE-common parameters, such asa subframe number or a total number of CCEs in a subframe, andUE-specific parameters such as the C-RNTI. For example, for a CCEaggregation level Lε{1, 2, 4, 8} CCEs, the CCEs corresponding to PDCCHcandidate m are given by:

CCEs for PDCCH candidate m=L·{(Y _(k) +m)mod└N _(CCE,k) /L┘}+i  Equation(1)

In Equation 1, N_(CCE,k) is the total number of CCEs in subframe k, i=0,. . . , L−1, m=0, . . . , M_(C) ^((L))−1, and M_(C) ^((L)) is the numberof PDCCH candidates to monitor in the UE-DSS. Exemplary values of M_(C)^((L)) for Lε{1, 2, 4, 8} are, respectively, {6, 6, 2, 2}. For theUE-DSS, Y_(k)=(A·Y_(k-1))mod D where Y⁻¹=C−RNTI≠0, A=39827 and D=65537.For the CSS, Y_(k)=0.

The DL control region in FIG. 1 is assumed to occupy a maximum ofM_(symb) ^(DL)=3 subframe symbols and a PDCCH is transmittedsubstantially over the entire DL BW. This configuration limits PDCCHcapacity of the DL control region and cannot support interferencecoordination in the frequency domain among PDCCH transmissions fromdifferent NodeBs. Expanded PDCCH capacity or PDCCH interferencecoordination in the frequency domain is needed in several cases. Onesuch case is the use of Remote Radio Heads (RRHs) in a network where aUE may receive DL signals either from a macro-NodeB or from an RRH. Ifthe RRHs and the macro-NodeB share the same cell identity, cellsplitting gains do not exist and expanded PDCCH capacity is needed toaccommodate PDCCH transmissions from the macro-NodeB and the RRHs.Another case exists regarding heterogeneous networks where DL signalsfrom a pico-NodeB experience strong interference from DL signals from amacro-NodeB, and interference coordination in the frequency domain amongthe NodeBs is needed.

A direct extension of the legacy DL control region to more than M_(symb)^(DL)=3 subframe symbols is not possible at least due to the requirementto support legacy UEs which are not aware of nor support such anextension. An alternative is to support DL control signaling in theconventional PDSCH region by using individual PRBs to transmit controlchannels. A PDCCH transmitted in PRBs of the conventional PDSCH regionwill be referred to as Enhanced PDCCH (EPDCCH).

FIG. 5 is a diagram illustrating an EPDCCH transmission structure in aDL TTI according to the related art.

Referring to FIG. 5, although EPDCCH transmissions 500 start immediatelyafter the legacy PDCCHs 510 and are over all remaining subframe symbols,they may instead always start at a fixed location, such as the fourthsubframe symbol, and extend over a part of the remaining subframesymbols. EPDCCH transmissions occur in four PRBs, 520, 530, 540, and 550while the remaining PRBs are used for PDSCH transmissions 560, 562, 564,566, 568.

A UE can be configured by higher layer signaling the PRBs that mayconvey EPDCCHs. The transmission of an EPDCCH to a UE may be in a singlePRB, if a NodeB has accurate CSI for the UE and can perform FrequencyDomain Scheduling (FDS) or beam-forming, or it may be in multiple PRBsif accurate CSI is not available at the NodeB or if the EPDCCH isintended for multiple UEs. An EPDCCH transmission over a single PRB (ora few PRBs contiguous in frequency) will be referred to herein aslocalized or non-interleaved, whereas an EPDCCH transmission overmultiple non-contiguous in frequency PRBs will be referred to herein asdistributed or interleaved.

The exact EPDCCH search space design is not material to the claimedinvention and may or may not follow the same principles as the PDCCH. AnEPDCCH consists of respective CCEs referred to as Enhanced CCEs (ECCEs),and a number of EPDCCH candidate locations exist for each possible ECCEaggregation level L_(E). For example, L_(E)ε{1, 2, 4} ECCEs forlocalized EPDCCHs and L_(E)ε{1, 2, 4, 8} ECCEs for distributed EPDCCHs.An ECCE may or may not have a same size as a legacy CCE, and an ECCE fora localized EPDCCH may or may not have a same size as an ECCE for adistributed EPDCCH.

Several aspects for the combined PDCCH and EPDCCH operation in FIG. 5need to be defined in order to provide a functional operation. Oneaspect is the process for UE scheduling. As a legacy UE cannot receiveEPDCCHs, support of PDCCHs needs to be maintained. However, in manycases, for example in heterogeneous networks, a UE may not be able toreliably receive PDCCHs, or PDCCHs may not exist. Duplicating thetransmission of a same DCI format in a PDCCH and an EPDCCH will increasethe respective overhead and should be avoided. Moreover, for networkswhere a macro-NodeB and pico-NodeBs share a same cell identity, thecapacity of the legacy CSS may not be sufficient to convey TPC commandsto all UEs in the coverage area of the macro-NodeB.

FIG. 6 is a diagram illustrating a network supporting with a same cellidentity a macro-NodeB and several pico-NodeBs according to the relatedart.

Referring to FIG. 6, network 600 includes UE 1 610 which communicateswith pico-NodeB#1 615. UE 2 620 communicates with pico-NodeB#2 625. UE 3630 communicates with pico-NodeB#3 635. Finally, UE 4 640 communicateswith the macro-NodeB 645. Although UE1, UE2, and UE3 are within thecoverage area of the macro-NodeB, capacity issues may exist for relyingon PDCCH from the macro-NodeB due to the resource limitation of thelegacy DL control region. In particular, although all UEs in thecoverage area of the macro-NodeB can receive SI, RA response, or pagingfrom the macro-NodeB, regardless whether a UE is associated with apico-NodeB or with the macro-NodeB, the macro-NodeB may not be able totransmit TPC commands to all UEs in its coverage area. Due to thelimited number of CCEs in the legacy CSS, transmission of multiplePDCCHs to convey TPC commands to UEs communicating with the pico-NodeBsmay not be possible. Moreover, a pico-NodeB cannot transmit its ownPDCCHs, as they will interfere with the PDCCHs transmitted by themacro-NodeB.

FIG. 7 is a diagram illustrating an interference co-ordination method ina heterogeneous network according to the related art.

Referring to FIG. 7, heterogeneous network 700 includes UE 1 710 whichcommunicates with pico-NodeB#1 715. UE 2 720 communicates withpico-NodeB#2 725. Finally, UE 3 730 communicates with a macro-NodeB 735.As the macro-NodeB transmits with much larger power than a pico-NodeB, asignal reception at a UE communicating with a pico-NodeB and locatednear the edge of the coverage area of the pico-NodeB will experiencesignificant interference from signals transmitted by the macro-NodeB. Toavoid such interference, the macro-NodeB may blank the transmission ofsome or all of its signals in certain subframes which can then be usedby pico-NodeBs to transmit to UEs located near the edge of therespective coverage areas. For example, the macro-NodeB 740 maysubstantially reduce (and even nullify) the transmission power of someor all of its signals in subframe 1 745 while transmitting signals withtheir nominal power in other subframes, while a pico-NodeB may transmitsignals with their nominal power in all subframes 750. Subframe 1 isreferred to as an Almost Blank Subframe (ABS). ABSs are transparent toUEs and are communicated among NodeBs over an X2 interface in order tofacilitate Inter-Cell Interference Coordination (ICIC). ABSs andnon-ABSs are indicated using a bitmap spanning a number of subframessuch as twenty, forty, or seventy subframes, with a binary 0 indicating,for example, a non-ABS and a binary 1 indicating an ABS.

Another aspect is a variation in a number of REs available for EPDCCHtransmissions per PRB, for example, depending on a size of the legacy DLcontrol region, defined by the number of M_(symb) ^(DL) subframe symbolsin FIG. 1, on the existence of CSI-RS REs, on the number of CRS REs,DMRS REs, and so on. This variation can be addressed either bymaintaining a same ECCE size and having a variable number of ECCEs perPRB (and possibly also having some REs that cannot be allocated to anECCE) or by maintaining a same number of ECCEs per PRB and having avariable ECCE size.

FIG. 8 is a diagram illustrating variations in an average ECCE size perPRB according to the related art.

Referring to FIG. 8, in a first realization of the contents of a PRB810, the legacy DL control region spans the first three subframe symbols820 and there is a first number of DMRS REs 830, CSI-RS REs 832, and CRSREs 834. For 4 ECCEs per PRB, the average number of REs per ECCE is 21.In a second realization of the contents of a PRB 850, the legacy DLcontrol region spans the first two subframe symbols 860 and there is asecond number of DMRS REs 870 and CRS REs 872 (no CSI-RS REs). For 4ECCEs per PRB, the average number of REs per ECCE is 27, or about 29%more than in the first realization. Larger variations in the ECCE sizemay also exist as the size of the DL control region may be even smallerthan 2 OFDM symbols and the number of CRS REs may further decrease.

Therefore, a need exists to define a set of subframes where a UE decodesPDCCH and another set of subframes where the UE decodes EPDCCH.

Another need exists to support transmissions of EPDCCHs in a set ofPRBs, from one or more sets of PRBs, while allowing the number of thesets PRBs to vary per subframe.

Yet another need exists to support transmissions of EPDCCHs in one ormore ECCEs while allowing a number of REs in an ECCE that can be used totransmit an EPDCCH to vary per subframe.

The above information is presented as background information only toassist with an understanding of the present disclosure. No determinationhas been made, and no assertion is made, as to whether any of the abovemight be applicable as prior art with regard to the present invention.

SUMMARY OF THE INVENTION

Aspects of the present invention are to address at least theabove-mentioned problems and/or disadvantages and to provide at leastthe advantages described below. Accordingly, an aspect of the presentinvention is to provide methods and apparatus for a User Equipment (UE)to decode a Physical Downlink Control CHannel (PDCCH) in a TransmissionTime Interval (TTI).

In accordance with an aspect of the present invention, a method for a UEcommunicating with a base station receives either a first type of aPDCCH or a second type of a PDCCH (e.g., Enhanced PDCCH (EPDCCH)) in aTTI, the first type of PDCCH and the second type of PDCCH conveyingrespectively Downlink Control Information (DCI) formats containingCyclic Redundancy Check (CRC) bits scrambled with a same type of a RadioNetwork Temporary Identifier (RNTI) is provided. The method includesreceiving by the UE a first bitmap associated with a number of TTIsequal to the first bitmap size, wherein each element of the first bitmapindicates whether a TTI is of a first type or of a second type, decodingby the UE only PDCCH of the first type if the TTI is of the first type,and decoding by the UE only PDCCH of the second type if the TTI is ofthe second type.

In accordance with another aspect of the present invention, a method fora UE communicating with a base station to receive a PDCCH transmitted bythe base station in Resource Elements (REs) of a set of PhysicalResource Blocks (PRBs), a single PRB of the set of PRBs comprising anumber of frequency sub-carriers over a TTI, using an aggregation levelof L Control Channel Elements (CCEs) in one of M^((L)) candidate PDCCHlocations, is provided. The method includes determining by the UEwhether the number of REs in a PRB available for transmitting PDCCHs issmaller than a predetermined number, determining by the UE a firstnumber of M^((L)) candidate PDCCH locations for decoding respectivePDCCHs if the number of REs in a PRB available for transmitting PDCCHsis smaller than the predetermined number, and determining by the UE asecond number of M^((L)) candidate PDCCH locations for decodingrespective PDCCHs if the number of REs in a PRB available fortransmitting PDCCHs is larger than or equal to the predetermined numberwherein the first number is different than the second number.

In accordance with yet another aspect of the present invention, a UEapparatus for receiving either a first type of a PDCCH or a second typeof a PDCCH transmitted by a base station in a TTI, the first type ofPDCCH and the second type of PDCCH conveying respective Downlink ControlInformation (DCI) formats containing CRC bits scrambled with a same typeof a RNTI, is provided. The apparatus includes a receiver configured toreceive a first bitmap associated with a number of TTIs equal to thefirst bitmap size, wherein each element of the first bitmap indicateswhether a TTI is of a first type or of a second type, and a detectorconfigured to detect only PDCCH of the first type if the TTI is of thefirst type, and to detect only PDCCH of the second type if the TTI is ofthe second type.

In accordance with still another aspect of the present invention, anapparatus for receiving a PDCCH transmitted by a base station in REs ofa set of PRBs, a single PRB of the set of PRBs comprising of a number offrequency sub-carriers over a TTI, using an aggregation level of L CCEsin one of M^((L)) candidate PDCCH locations is provided. The apparatusincludes a comparator configured to determine whether the number of REsin a PRB available for transmitting PDCCHs is smaller than apredetermined number, a searcher configured to determine a first numberof M^((L)) candidate PDCCH locations if the number of REs in a PRBavailable for transmitting PDCCHs is smaller than the predeterminednumber or to determine a second number of M^((L)) candidate PDCCHlocations if the number of REs in a PRB available for transmittingPDCCHs is larger than or equal to the predetermined number wherein thefirst number is different than the second number, and a decoderconfigured to decode PDCCHs in the respective candidate PDCCH locations.

Other aspects, advantages, and salient features of the invention willbecome apparent to those skilled in the art from the following detaileddescription, which, taken in conjunction with the annexed drawings,discloses exemplary embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a structure for a DownLink (DL)Transmission Time Interval (TTI) according to the related art;

FIG. 2 is a block diagram illustrating an encoding process for a DLControl Information (DCI) format according to the related art;

FIG. 3 is a block diagram illustrating a decoding process for a DCIformat according to the related art;

FIG. 4 is a diagram illustrating a transmission process of DCI formatsin respective Physical DL Control Channels (PDCCHs) according to therelated art.

FIG. 5 is a diagram illustrating an Enhanced PDCCH (EPDCCH) transmissionstructure in a DL TTI according to the related art;

FIG. 6 is a diagram illustrating a network supporting with a same cellidentity a macro-NodeB and several pico-NodeBs according to the relatedart;

FIG. 7 is a diagram illustrating an interference co-ordination method ina heterogeneous network according to the related art.

FIG. 8 is a diagram illustrating variations in an average EnhancedControl Channel Element (ECCE) size per Physical Resource Block (PRB)according to the related art;

FIG. 9 is a diagram illustrating a conditional transmission of EPDCCHsaccording to an exemplary embodiment of the present invention.

FIG. 10 illustrates decoding operations a User Equipment (UE) performsto detect EPDCCHs and PDCCHs conveying DCI formats with CyclicRedundancy Check (CRC) scrambled by System Information (SI)-RadioNetwork Temporary Identifier (RNTI), Random Access (RA)-RNTI, PDSCH(P)-RNTI, or Cell (C)-RNTI according to an exemplary embodiment of thepresent invention;

FIG. 11 is a diagram illustrating a process for a UE to perform decodingoperations in a legacy Common Search Space (CSS) and in an enhanced CSSaccording to an exemplary embodiment of the present invention;

FIG. 12 is a diagram illustrating a process for using different sets ofPRBs for EPDCCH transmissions in respectively different sets ofsubframes according to an exemplary embodiment of the present invention;

FIG. 13 is a diagram illustrating a process for a UE to determine anumber of EPDCCH candidates for a respective ECCE aggregation leveldepending on a number of available Resource Elements (REs) per PRBaccording to an exemplary embodiment of the present invention;

FIG. 14 illustrates a process for a UE to determine a number of PRBsused for EPDCCH transmissions and an allocation of ECCEs depending on anumber of available REs per PRB for EPDCCH transmissions according to anexemplary embodiment of the present invention; and

FIG. 15 illustrates a UE decoder for detecting a DCI format conveyed byan EPDCCH in accordance to one or more conditions including a number ofPRBs that can be used for EPDCCH transmissions, a number of candidatesper ECCE aggregation level, or a number of PRBs in a cluster of PRBsused for EPDCCH transmissions according to an exemplary embodiment ofthe present invention.

Throughout the drawings, it should be noted that like reference numbersare used to depict the same or similar elements, features, andstructures.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The following description with reference to the accompanying drawings isprovided to assist in a comprehensive understanding of exemplaryembodiments of the invention as defined by the claims and theirequivalents. It includes various specific details to assist in thatunderstanding but these are to be regarded as merely exemplary.Accordingly, those of ordinary skill in the art will recognize thatvarious changes and modifications of the embodiments described hereincan be made without departing from the scope and spirit of theinvention. In addition, descriptions of well-known functions andconstructions may be omitted for clarity and conciseness.

The terms and words used in the following description and claims are notlimited to the bibliographical meanings, but, are merely used by theinventor to enable a clear and consistent understanding of theinvention. Accordingly, it should be apparent to those skilled in theart that the following description of exemplary embodiments of thepresent invention is provided for illustration purpose only and not forthe purpose of limiting the invention as defined by the appended claimsand their equivalents.

It is to be understood that the singular forms “a,” “an,” and “the”include plural referents unless the context clearly dictates otherwise.Thus, for example, reference to “a component surface” includes referenceto one or more of such surfaces.

By the “substantially” it is meant that the recited characteristic,parameter, or value need not be achieved exactly, but that deviations orvariations, including for example, tolerances, measurement error,measurement accuracy limitations and other factors known to those ofskill in the art, may occur in amounts that do not preclude the effectthe characteristic was intended to provide.

Additionally, although exemplary embodiments of the present inventionwill be described below with reference to Orthogonal Frequency DivisionMultiplexing (OFDM), they also are applicable to all Frequency DivisionMultiplexing (FDM) transmissions in general and to Discrete FourierTransform (DFT)-spread OFDM in particular.

A first exemplary embodiment considers methods and apparatus forproviding a DownLink (DL) Control Information (DCI) format schedulingUser Equipment (UE)-common DCI or UE-dedicated DCI either by an EnhancedPhysical DL Control Channel (EPDCCH) or by a Physical DL Control Channel(PDCCH) but not with both in a same subframe. As it is subsequentlydescribed in the context of Almost Blank Subframe (ABS), this isachieved by a NodeB signaling to the UE a bitmap indicating, over anumber of subframes equal to the bitmap size, the subframes where the UEshould monitor PDCCH and the subframes where the UE should monitorEPDCCH. The existence of an EPDCCH conveying a DCI format schedulingUE-common DCI (or UE-dedicated DCI) to a UE is conditioned on theexistence of a respective PDCCH with a desired reliability or capacity.

In a heterogeneous network, a macro-NodeB may use ABSs for Inter-CellInterference Coordination (ICIC) purposes in order to enable UEscommunicating with pico-NodeBs that are in the coverage area of themacro-NodeB and nominally experience strong interference by signalstransmitted by the macro-NodeB to reliably receive signals from theirrespective pico-NodeBs. In an ABS, the macro-NodeB substantially reducesthe transmission power of some signals, including suspendingtransmissions, in order to avoid creating interference to susceptibleUEs that communicate with pico-NodeBs.

A PDCCH conveying a DCI format scheduling UE-common DCI from amacro-NodeB needs to be reliably received by multiple UEs, includingpossibly all UEs in the coverage area of the macro-NodeB. These UEs maybe experiencing a wide range of respective Signal-to-Interference andNoise Ratio (SINR) reflecting respective PDCCH detection reliabilities.Consequently, a PDCCH conveying a DCI format scheduling UE-common DCI toa group of UEs should be preferably transmitted with its nominal powerin order to ensure the desired detection reliability at the UE, in agroup of UEs, experiencing the worst SINR. Therefore, UEs communicatingwith the macro-NodeB cannot be scheduled, in practice, for UE-common DCIduring ABSs. The same applies in practice for UE-dedicated DCI which amacro-NodeB cannot typically transmit in ABSs.

To avoid the above limitations, the macro-NodeB may transmit EPDCCHsproviding UE-common DCI, such as System Information (SI), Random Access(RA) response, paging, or UE-dedicated DCIs in ABSs. To avoidduplicating the transmission of a DCI format scheduling UE-common DCI, amacro-NodeB in a non-ABS may convey such DCI format using only PDCCHs.As a PDCCH substantially spans the entire DownLink (DL) BandWidth (BW)and its detection at a UE is based on a Common Reference Signal (CRS),then, for the same transmission power and coding rate, a PDCCH istypically more reliable than a distributed EPDCCH which may experienceworse frequency diversity because it only spans a few Physical ResourceBlocks (PRBs) and detects the EPDCCH using a worse channel estimationthat is based on a DeModulation Reference Signal (DMRS) contained inthose PRBs.

FIG. 9 is a diagram illustrating a conditional transmission of EPDCCHsaccording to an exemplary embodiment of the present invention.

Referring to FIG. 9, in a frame consisting of ten subframes, subframe 0900, subframe 2 902, subframe 4 904, subframe 5 905, and subframe 9 909are configured to a UE as non-ABSs, whereas subframe 1 901, subframe 3903, subframe 6 906, subframe 7 907, and subframe 8 908 are configuredto a UE as ABSs. The configuration is through a respective bitmap ofsize 10. In an ABS, such as subframe 1, the macro-NodeB transmits withreduced power, including suspending transmission (zero power), PDCCHs910 and Physical DL Shared Channels (PDSCHs) in some Resource Blocks(RBs) 915. The macro-NodeB transmits EPDCCHs with their nominal power intheir respective RBs 920 and 925. As transmission of PDCCHs may notexist, or may be with reduced power, transmission of DCI formats withCyclic Redundancy Check (CRC) scrambled by SI-Radio Network TemporaryIdentifier (RNTI), RA-RNTI, PDSCH (P)-RNTI, or Cell (C)-RNTI may beperformed by EPDCCHs. The macro-NodeB may also transmit with nominalpower PDSCHs in respective PRBs 930 where, in practice, pico-NodeBs donot transmit PDSCHs to respective UEs experiencing strong interferencefrom the macro-NodeB. Conversely, in non-ABSs such as subframe 5, themacro-NodeB transmits PDCCHs with nominal power 940. The macro-NodeB mayalso transmit with nominal power EPDCCHs (for some UEs) in respectivePRBs 950, 952, 954, 956, and 960. Due to the transmission of PDCCHs withnominal power, EPDCCHs need not convey DCI formats with CRC scrambled bySI-RNTI, RA-RNTI, P-RNTI, or C-RNTI which are instead conveyed byPDCCHs.

To obtain a DCI format scheduling UE-common DCI (such as SI, RAresponse, or paging), or UE-dedicated DCI, a UE performs decodingoperations for respective EPDCCHs (with CRC scrambled with a SI-RNTI,RA-RNTI, P-RNTI, or C-RNTI respectively,) in an enhanced Common SearchSpace (CSS) or in an enhanced UE-DSS, respectively, in ABS subframes andperforms decoding operations for respective PDCCHs (with CRC scrambledwith a SI-RNTI, RA-RNTI, P-RNTI, or C-RNTI) in the legacy CSS or in thelegacy UE-DSS, respectively, in non-ABS subframes.

FIG. 10 illustrates decoding operations a UE performs to detect EPDCCHsand PDCCHs conveying DCI formats with CRC scrambled by SI-RNTI, RA-RNTI,P-RNTI, or C-RNTI according to an exemplary embodiment of the presentinvention.

Referring to FIG. 10, in decoding operation 1000, a UE performs decodingoperations to detect EPDCCHs and PDCCHs conveying DCI formats with CRCscrambled by SI-RNTI, RA-RNTI, P-RNTI, or C-RNTI, depending on theconfigured subframe type 1010. The UE decoder may be, for example, asdescribed in FIG. 3 with the following additional controller functions.If the subframe is an ABS, DCI formats scheduling UE-common DCI orUE-dedicated DCI may be provided only by EPDCCHs and a UE may performdecoding operations for these EPDCCHs only in an enhanced CSS 1020 or inan enhanced UE-DSS. If the subframe is not an ABS, DCI formatsscheduling UE-common DCI or UE-dedicated DCI may be provided only byPDCCHs and a UE performs decoding operations for these PDCCHs only in alegacy CSS 1030 or in a legacy UE-DSS.

The use of ABS without the use of EPDCCHs may limit the number of DL orUL Hybrid Automatic Repeat reQuest (HARQ) processes that can besupported by a macro-NodeB for most UEs due to an inability of themacro-NodeB to schedule PDSCH or PUSCH, in an ABS. Using EPDCCH andinterference coordination in the frequency domain (across RBs) among themacro-NodeB and the pico-NodeBs allows the use of all HARQ processes andimproved system operation. However, the transmission of ACKnowledgement(ACK) signals for an HARQ process (HARQ-ACK signals) from themacro-NodeB in response to receptions of data information in respectivePUSCHs may be limited in ABS due to, for example, the absence of, or dueto power limitations of HARQ-ACK signaling. The same approach as for thetransmission of DCI formats by respective EPDCCHs can also be followedin this case. If the subframe where an HARQ-ACK signal is to betransmitted by the macro-NodeB is configured to a UE as an ABS, thetransmission can occur in PRBs configured for EPDCCH transmissions byusing some Resource Elements (REs) to transmit HARQ-ACK signals.Otherwise, if the subframe where an HARQ-ACK signal is to be transmittedby the macro-NodeB is configured to the UE as a non-ABS, thetransmission of the HARQ-ACK signal occurs as usual in the legacy DLcontrol region (by allocating some REs to HARQ-ACK signaltransmissions).

In addition to PDCCHs or EPDCCHs providing DCI formats schedulingtransmission of UE-common DCI or UE-dedicated DCI, PDCCHs or EPDCCHs mayonly provide Transmission Power Control (TPC) commands to a group of UEs(without scheduling a respective PDSCH or PUSCH) through a DCI formatwith CRC scrambled by a TPC-RNTI. Each TPC command in the group of TPCcommands is intended for a UE in the group of UEs and each UE isconfigured the placement in the DCI format of the TPC command intendedfor it. In order to avoid duplication in the transmission of a DCIformat with CRC scrambled by a TPC-RNTI by both a PDCCH and an EPDCCHand avoid the capacity limitations of a legacy CSS, a UE can beconfigured whether to perform respective decoding operations either forPDCCHs or for EPDCCHs. Capacity limitation of the legacy CCS may occuras, for example, a legacy CSS may consist of only 16 Control ChannelElements (CCEs) which may need to be used in a subframe to transmitPDCCHs with CRCs scrambled by SI-RNTIs, RA-RNTIs, P-RNTIs, or TPC-RNTIs.Without considering the existence of ABS, the transmission of DCIformats with CRCs scrambled with a SI-RNTI, or RA-RNTI, or P-RNTI may beexclusively performed by PDCCHs, while a UE may be configured based onwhether the transmission of a DCI format scrambled with a TPC-RNTI is bya PDCCH or by an EPDCCH. Therefore, a UE may monitor a legacy CSS forDCI formats with CRC scrambled with a SI-RNTI, a RA-RNTI, or a P-RNTI,but it can be configured to monitor either a legacy CSS (PDCCH) or anenhanced CSS (EPDCCH) for a DCI format with CRC scrambled with aTPC-RNTI (or, in general, with another UE-common RNTI).

FIG. 11 is a diagram illustrating a process for a UE to perform decodingoperations in a legacy CSS and in an enhanced CSS according to anexemplary embodiment of the present invention.

Referring to FIG. 11, in a process for UE to perform decoding operations1100, a UE (in non-ABS) always performs decoding operations for PDCCHsin a legacy CSS in order to potentially detect DCI formats with CRCscrambled with SI-RNTI, RA-RNTI, or P-RNTI. However, for a DCI formatscrambled with a TPC-RNTI, the UE is configured to either performdecoding operations for PDCCHs in a legacy CSS, or for EPDCCHs in anenhanced CSS 1110. The UE decoder may be, for example, as described inFIG. 3 with the following additional controller functions. If a UE isconfigured 1120 to perform decoding operations of PDCCHs for a DCIformat with CRC scrambled by a TPC-RNTI, the UE may monitor a legacy CSSand not perform decoding operations of EPDCCHs in an enhanced CSS forsuch DCI format 1130. If a UE is configured to perform decodingoperations of EPDCCHs for a DCI format with CRC scrambled by a TPC-RNTI,the UE may monitor an enhanced CSS and not perform decoding operationsof PDCCHs in a legacy CSS for such DCI format 1140.

A size of the DCI format with CRC scrambled by a TPC-RNTI is designed tobe same as a size of DCI formats with CRC scrambled by a C-RNTI thatschedule PDSCH (DCI format 1A) or PUSCH (DCI format 0) when a networkhas little information about channel conditions that a UE isexperiencing or, in general, when the network wants to provide the mostrobust and reliable detection for a PDSCH or a PUSCH. These DCI formatswith CRC scrambled by a C-RNTI are the only formats transmitted in aCSS. By having a same DCI format size and differing only in thescrambling of a CRC (either by TPC-RNTI or by C-RNTI), a UE candetermine with a single decoding operation whether any of these DCIformats was conveyed in a candidate PDCCH or EPDCCH. In order to avoidincreasing a maximum number of decoding operations a UE needs to performin a subframe, a UE may assume that the transmission of these DCIformats (with CRC scrambled by a TPC-RNTI or by a C-RNTI) is always in asame CSS (either legacy or enhanced) and that a UE does not performadditional decoding operations in another CSS to determine whether therewas a DCI format with CRC scrambled by a C-RNTI transmitted to it.

A second exemplary embodiment of the invention considers transmissionand detection processes for EPDCCHs when a number of REs available forEnhanced CCEs (ECCEs) per PRB varies across subframes.

A first consequence of variations across subframes in a number of REsper PRB for available transmissions of EPDCCHs is that an average numberof EPDCCHs that can be supported may also vary as the respectiveresources vary. To reduce variations in an average number of EPDCCHsthat can be transmitted per subframe, a UE can be configured with atleast two sets of PRBs to monitor for potential EPDCCH transmissionsdepending on a number of respective REs available for EPDCCHtransmissions per PRB. This number of REs may be different betweendistributed EPDCCH and localized EPDCCH transmissions (in case the PRBsfor distributed EPDCCHs are not dynamically determined through thetransmission of additional information, similar to the subframe symbolsfor PDCCH transmissions).

For example, when there are REs allocated for Channel StateInformation-Reference Signal (CSI-RS) transmission or for interferencemeasurements in a subframe or when there are fewer subframe symbols forEPDCCH transmissions per subframe (in case the starting symbol of EPDCCHtransmissions varies per subframe), a number of EPDCCH REs per PRB maybe below a predetermined value and a UE may then consider a first set ofPRBs for transmissions of EPDCCHs; otherwise, the UE may consider asecond set of PRBs wherein the number of PRBs in the first set can belarger than the number of PRBs in the second set.

In a first exemplary method, a UE may dynamically determine (on asubframe basis) which set of PRBs (first set or second set) to considerfor EPDCCH transmissions as a number of REs available for EPDCCHtransmissions dynamically varies per PRB per subframe. For example, a UEmay determine a starting subframe symbol for EPDCCH transmissions bydetecting a channel transmitted in a first subframe symbol and informinga number of subframe symbols for a legacy DL control region. The UE maythen consider a first set of PRBs for EPDCCH transmissions if a legacyDL control region spans 3 subframe symbols and a second set of PRBs forEPDCCH transmissions if the legacy DL control region spans 1 or 2subframe symbols.

FIG. 12 is a diagram illustrating a process for using different sets ofPRBs for EPDCCH transmissions in respectively different sets ofsubframes according to an exemplary embodiment of the present invention.

Referring to FIG. 12, in process 1200, a number of REs per PRB availablefor EPDCCH transmissions is compared to a predetermined value V₁ 1210.If this number of REs is smaller than V₁, a first set of PRBs 1220consisting of a first number of PRBs 1230, 1232, 1234, 1236, 1238 isused for EPDCCH transmissions in the given subframe. Otherwise, if thisnumber of REs is not smaller than V₁, a second set of PRBs 1240consisting of a second number of PRBs 1250, 1252, 1254, 1256, 1258 isused for EPDCCH transmissions in the given subframe.

For EPDCCH transmissions there are additional implications from thevariation in the available number of REs per PRB. If a variable ECCEsize is used to maintain a same number of ECCEs per PRB, regardless ofthe number of REs in a PRB, the detection reliability of an EPDCCHcorresponding to a given ECCE aggregation level also varies. Forexample, transmission of a DCI format using an EPDCCH consisting of oneECCE may be possible when the number of REs per ECCE has a first valuebut may not be possible when the number of REs per ECCE has a second(smaller) value as the code rate in the latter case may approach or evenexceed one. If a same ECCE size is used, a number of ECCEs per PRBvaries.

In a second exemplary method, to circumvent the above shortcoming eitherwhen an ECCE size is variable or when it is constant, a UE may beconfigured at least two sets of EPDCCH candidates for respective ECCEaggregation levels in at least two respective sets of subframes in orderto achieve adaptation to variations in a number of REs for EPDCCHtransmissions per PRB. For example, for L_(E)ε{1, 2, 4} ECCEs, a firstset of respective EPDCCH candidates M_(symb) ^(DL)ε{M_(E) ⁽¹⁾, M_(E)⁽²⁾, M_(E) ⁽⁴⁾)} can be M_(E) ^((L) ^(E) ⁾ε{2, 4, 2} if a number of REsper ECCE is smaller than a predetermined value and can be M_(E) ^((L)^(E) ⁾ε{0, 6, 4} otherwise.

Alternatively, in subframes where an average ECCE size for EPDCCHtransmissions is below a predetermined value, some or all of thedecoding operations for the smaller ECCE aggregation levels may be addedto those for distributed EPDCCH transmissions. For example, a first setof EPDCCH candidates for localized EPDCCH transmissions may be M_(E)^((L) ^(E) ⁾ε{2, 4, 2} and a second set may be M_(E) ^((L) ^(E) ⁾ε{0, 2,2}. The missing candidates can be allocated to distributed EPDCCHtransmissions for which a respective first set of candidates can beM_(E) ^((L) ^(E) ⁾ε{2, 2, 2, 2} and a respective second set ofcandidates can be M_(E) ^((L) ^(E) ⁾ε{4, 4, 2, 2}. As previouslydiscussed for the case of the sets of configured PRBs for EPDCCHtransmissions, a UE may dynamically determine (on a subframe basis) aset of EPDCCH candidates to consider in a subframe as a number ofavailable REs per PRB per subframe also dynamically varies.

FIG. 13 is a diagram illustrating a process for a UE to determine anumber of EPDCCH candidates for a respective ECCE aggregation leveldepending on a number of available REs per PRB according to an exemplaryembodiment of the present invention.

Referring to FIG. 13, in process 1300, a UE first compares a number ofREs per PRB to a predetermined value V₂ 1310. If the number of REs perPRB is smaller than V₂, the UE considers EPDCCH candidates M_(E) ^((L)^(E) ^(,1))ε{M_(E) ^((1,1)), M_(E) ^((2,1)), M_(E) ^((4,1))} forrespective ECCE aggregation levels L_(E)ε{1, 2, 4} 1320. Otherwise, theUE considers EPDCCH candidates M_(E) ^((L) ^(E) ^(,2))ε{M_(E) ^((1,2)),M_(E) ^((2,2)), M_(E) ^((4,2))} for respective ECCE aggregation levelsL_(E)ε{1, 2, 4} 1330. The above process is applicable regardless ofwhether an ECCE size varies per subframe while a number of ECCEs per PRBremains same or whether a number of ECCEs per PRB varies per subframewhile an ECCE size remains same.

In a third exemplary method, to further increase the flexibility ofEPDCCH transmissions, as an ECCE size per PRB varies, or as a number ofECCEs per PRB varies, PRB clusters may be used when a number ofavailable REs for EPDCCH transmissions per PRB is smaller than apredetermined value. For example, if this number of REs is smaller thana predetermined value, a UE may consider that configured PRBs for EPDCCHtransmissions are actually contiguous clusters of PRBs (for example, theadditional PRBs can be symmetric relative to a configured PRB and startfrom the next PRB); otherwise, a UE may consider the configured PRBswith their nominal meaning (single PRBs). In case an EPDCCH transmissionis over multiple adjacent PRBs, a multiplexing of ECCEs can remain as inthe case an EPDCCH transmission is over a single PRB with the exceptionthat each ECCE spans the same multiple of REs relative to the case of asingle PRB. The same enhancement to the number of PRBs can be appliedwhere a first set of PRBs is used when a number of available REs per PRBfor EPDCCH transmissions has a first value (for example, when there isno CSI-RS transmission or the legacy DL control region has a first sizeassuming that a UE determines this size every subframe) and a second(larger) set of PRBs is used when a number of available REs per PRB forEPDCCH transmissions has a second (smaller) value (there is CSI-RStransmission or the legacy DL control region has a second size largerthan the first size). This is because the number of REs per PRB that isavailable for EPDCCH transmissions decreases when there is CSI-RStransmission of when the legacy DL control region has a larger size andthis decrease can be compensated by proportionally increasing the numberrespective RBs.

FIG. 14 illustrates a process for a UE to determine a number of PRBsused for EPDCCH transmissions and an allocation of ECCEs depending on anumber of available REs per PRB for EPDCCH transmissions according to anexemplary embodiment of the present invention.

Referring to FIG. 14, in process 1400, a UE first compares a number ofREs per PRB to a predetermined value V₃ 1410. If the number of REs perPRB is not smaller than V₃, the UE may consider localized EPDCCHtransmissions per single PRB per subframe 1420. Without explicitlyillustrating the REs for CRS/DMRS/CSI-RS or transmissions of othersignals, there are 4 ECCEs per PRB 1430, 1432, 1434, 1436. Otherwise, ifthe number of REs per PRB is smaller than V₃, the UE may considerlocalized EPDCCH transmissions per two PRBs 1440 and there are 2 ECCEsper PRB. The number and structure of ECCEs 1450, 1452, 1454, 1456 may bethe same as in the case of EPDDCHs that are transmitted per PRB, buteach ECCE spans twice the number of REs.

In the previous three exemplary methods, the respective predeterminedvalues may be either signaled to a UE by the NodeB, or may be determinedby the UE based on the number of information bits (payload) for each DCIformat that the UE is configured to decode. For example, for the thirdexemplary embodiment, the number of REs per PRB may be adequate for apayload of a first DCI format, but may not be adequate for a payload ofa second DCI format. The predetermined value may be a code rateachievable for a respective DCI format transmission over a referencenumber of ECCEs such as 1 ECCE. A UE may then consider a single PRB inthe former case and consider a cluster of two PRBs in the latter case.

The previous three exemplary methods may also be combined. For example,for the second and third methods, when a UE determines (based on anumber of REs in a PRB for EPDCCH transmissions) that localized EPDCCHtransmissions are over a single PRB (4 ECCEs per PRB), it may alsoconsider a first set of EPDCCH candidates for a first set of ECCEaggregation levels while when it determines that localized EPDCCHtransmissions are over 2 PRBs (2 ECCEs per PRB), and it may consider asecond set of EPDCCH candidates for a second set of ECCE aggregationlevels.

The description for each of the previous three methods is made withrespect to a UE determining on a subframe basis a condition based onwhich it determines a parameter set to apply for detections of EPDCCHs.However, each of the previous three methods may also apply in case inwhich a UE does not determine on a subframe basis the parametersaffecting that condition, such as, for example, if a UE does notdetermine a size of the legacy DL control region per subframe. In suchcase, a parameter set for a respective method may be configured to theUE by a NodeB through higher layer signaling. For example, if a UE isconfigured to assume a legacy DL control region size of 1 or 2 subframesymbols, a first set of parameters is also implicitly configured for arespective method (such as a single PRB in case of the third method)while if a UE is configured to assume a legacy DL control region size of3 subframe symbols, a second set of parameters is implicitly configuredfor the respective method (such as a cluster of 2 PRBs in case of thethird method). The configuration can also be dependent on the subframe.For example, in a subframe with no CSI-RS transmission, a first set ofparameters can be configured for a respective method; otherwise, asecond set of parameters can be configured for a respective method.

FIG. 15 illustrates a UE decoder for detecting a DCI format conveyed byan EPDCCH in accordance to one or more conditions including a number ofPRBs that can be used for EPDCCH transmissions, a number of candidatesper ECCE aggregation level, or a number of PRBs in a cluster of PRBsused for EPDCCH transmissions according to an exemplary embodiment ofthe present invention.

Referring to FIG. 15, in process 1500, a UE first determines a number ofPRBs, a number of EPDCCH candidates per ECCE aggregation level, or anumber of PRBs in a cluster of PRBs used for an EPDCCH transmission1510. This determination may be performed by the UE, or may beconfigured by a NodeB through higher layer signaling. Once the UEdetermines the resources (PRBs) for EPDCCH transmissions or the numberof candidates per respective ECCE aggregation level, a received controlsignal in a candidate EPDCCH 1520 is demodulated, resulting bits arede-interleaved 1530, a rate matching applied at a NodeB transmitter isrestored 1540, and data is subsequently decoded 1550. After decoding,DCI format bits 1570 are obtained after extracting CRC bits 1560 whichare then de-masked 1580 by applying an XOR operation with a RNTI 1585corresponding to the DCI format. Finally, the UE performs a CRC test1590. If the CRC test passes, the UE considers the DCI format as a validone and determines the parameters for signal reception in a PDSCH orsignal transmission in a PUSCH. If the CRC test does not pass, the UEdisregards the presumed DCI format.

While the present invention has been shown and described with referenceto certain exemplary embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the presentinvention as defined by the appended claims and their equivalents.

What is claimed is:
 1. A method for a User Equipment (UE) communicatingwith a base station to receive either a first type of a PhysicalDownlink Control CHannel (PDCCH) or a second type of a PDCCH in aTransmission Time Interval (TTI), the first type of PDCCH and the secondtype of PDCCH conveying respective Downlink Control Information (DCI)formats containing Cyclic Redundancy Check (CRC) bits scrambled with asame type of a Radio Network Temporary Identifier (RNTI), the methodcomprising: receiving by the UE a first bitmap associated with a numberof TTIs equal to the first bitmap size, wherein each element of thefirst bitmap indicates whether a TTI is of a first type or of a secondtype; decoding by the UE only PDCCH of the first type if the TTI is ofthe first type; and decoding by the UE only PDCCH of the second type ifthe TTI is of the second type.
 2. The method of claim 1, wherein thefirst bitmap has a same size as a second bitmap transmitted by the basestation over an X2 interface with other base stations, the second bitmapbeing associated with a number of TTIs equal to the second bitmap size,and wherein each element of the second bitmap indicates whether, in therespective TTI, the base station transmits signals with reduced power,nominal power or zero power.
 3. The method of claim 1, wherein thetransmission of the PDCCH of the first type in a first TTI is over anoperating bandwidth and over at most a predetermined number of TTIsymbols starting from the beginning of the TTI, and the transmission ofthe PDCCH of the second type in a second TTI is over a subset of theoperating bandwidth and over all symbols of the second TTI startingafter at most the predetermined number symbols from the beginning of theTTI.
 4. The method of claim 1, wherein the transmission of anacknowledgement signal from the base station to the UE, in response to areception by the base station of data information transmitted by the UE,is in resources in a first set of resources used to transmit PDCCH ofthe first type if the TTI is of the first type, and is in resources in asecond set of resources used to transmit PDCCH of the second type if theTTI is of the second type.
 3. The method of claim 1, wherein the UEreceives a first type of control information only by PDCCH of the firsttype, and receives a second type of control information only by PDCCH ofthe second type.
 6. The method of claim 5, wherein the first type ofcontrol information provides scheduling information for a transmissionof paging, random access response, or system information, and the secondtype of control information provides other information for more than oneUE.
 7. The method of claim 1, wherein the PDCCH of the first type istransmitted with a first aggregation level of Control Channel Elements(CCEs) of a first type, the PDCCH of the second type is transmitted witha second aggregation level of CCEs of a second type and the UE performsa different number of decoding operations for the PDCCH of the firsttype than for the PDCCH of the second type, and wherein the firstaggregation level is equal to the second aggregation level.
 8. A methodfor a User Equipment (UE) communicating with a base station to receive aPhysical Downlink Control CHannel (PDCCH) transmitted by the basestation in Resource Elements (REs) of a set of Physical Resource Blocks(PRBs), a single PRB of the set of PRBs comprising a number of frequencysub-carriers over a Transmission Time Interval (TTI), using anaggregation level of L Control Channel Elements (CCEs) in one of M^((L))candidate PDCCH locations, the method comprising: determining by the UEwhether the number of REs in a PRB available for transmitting PDCCHs issmaller than a predetermined number; determining by the UE a firstnumber of M^((L)) candidate PDCCH locations for decoding respectivePDCCHs if the number of REs in a PRB available for transmitting PDCCHsis smaller than the predetermined number; and determining by the UE asecond number of M^((L)) candidate PDCCH locations for decodingrespective PDCCHs if the number of REs in a PRB available fortransmitting PDCCHs is larger than or equal to the predetermined numberwherein the first number is different than the second number.
 9. Themethod of claim 8, wherein the predetermined number of REs in a PRB isdetermined so that the transmission of a Downlink Control Information(DCI) format in a PDCCH transmitted using one CCE is with apredetermined code rate.
 10. The method of claim 8, wherein for L=1, thefirst number of M^((L)) candidate PDCCH locations is zero, and thesecond number of M^((L)) candidate PDCCH locations is larger than zero.11. The method of claim 10, wherein for at least one value L>1, thefirst number of M^((L)) candidate PDCCH locations is larger than thesecond number of M^((L)) candidate PDCCH locations.
 12. The method ofclaim 8, wherein the UE determines the number of REs in a PRB availablefor transmitting PDCCHs in the TTI from the total number of REs in a PRBafter excluding at least REs used to transmit Common Reference Signals(CRS), Channel State Information Reference Signals (CSI-RS), and othercontrol channels.
 13. The method of claim 8, wherein the base stationtransmits PDCCH in one of two sets of PRBs configured to the UE forPDCCH transmissions through higher layer signaling.
 14. The method ofclaim 13, wherein the number of PRBs in the first set of PRBs is largerthan the number of PRBs in the second set of PRBs.
 15. The method ofclaim 14, wherein for at least one value of L, the number of PDCCHdecoding operations in the first set of PRBs is different than in thesecond set of PRBs.
 16. The method of claim 8, wherein the number ofCCEs in a PRB is two if the number of REs in a PRB available fortransmitting PDCCHs is smaller than the predetermined number, and thenumber of CCEs in a PRB is four otherwise.
 17. The method of claim 8,wherein the number of CCEs in a PRB is always four.
 18. A User Equipment(UE) apparatus for receiving either a first type of a Physical DownlinkControl CHannel (PDCCH) or a second type of a PDCCH transmitted by abase station in a Transmission Time Interval (TTI), the first type ofPDCCH and the second type of PDCCH conveying respective Downlink ControlInformation (DCI) formats containing Cyclic Redundancy Check (CRC) bitsscrambled with a same type of a Radio Network Temporary Identifier(RNTI), the apparatus comprising: a receiver configured to receive afirst bitmap associated with a number of TTIs equal to the first bitmapsize, wherein each element of the first bitmap indicates whether a TTIis of a first type or of a second type; and a detector configured todetect only PDCCH of the first type if the TTI is of the first type, andto detect only PDCCH of the second type if the TTI is of the secondtype.
 19. The apparatus of claim 18, wherein the first bitmap has a samesize as a second bitmap transmitted by the base station over an X2interface with other base stations, the second bitmap being associatedwith a number of TTIs equal to the second bitmap size, and wherein eachelement of the second bitmap indicates whether, in the respective TTI,the base station transmits signals with reduced power, nominal power orzero power.
 20. The apparatus of claim 18, wherein the transmission ofthe PDCCH of the first type in a first TTI is over an operatingbandwidth and over at most a predetermined number of TTI symbolsstarting from the beginning of the TTI, and the transmission of thePDCCH of the second type in a second TTI is over a subset of theoperating bandwidth and over all symbols of the second TTI startingafter at most the predetermined number symbols from the beginning of theTTI.
 21. The apparatus of claim 18, wherein the transmission of anacknowledgement signal from the base station to the apparatus inresponse to a reception by the base station of data informationtransmitted by the apparatus is in resources in a first set of resourcesused to transmit PDCCH of the first type if the TTI is of the firsttype, and in resources in a second set of resources used to transmitPDCCH of the second type if the TTI is of the second type.
 22. Theapparatus of claim 18, wherein the apparatus receives a first type ofcontrol information only by PDCCH of the first type and receives asecond type of control information only by PDCCH of the second type. 23.The apparatus of claim 22, wherein the first type of control informationprovides scheduling information for a transmission of paging, randomaccess response, or system information, and the second type of controlinformation provides other information for more than one UE apparatus.24. The apparatus of claim 18, wherein the PDCCH of the first type istransmitted with a first aggregation level of Control Channel Elements(CCEs) of the first type, the PDCCH of the second type is transmittedwith a second aggregation level of CCEs of the second type, and theapparatus performs a different number of decoding operations for thePDCCH of the first type than for the PDCCH of the second type, andwherein the first aggregation level is equal to the second aggregationlevel.
 25. A User Equipment (UE) apparatus for receiving a PhysicalDownlink Control CHannel (PDCCH) transmitted by a base station inResource Elements (REs) of a set of Physical Resource Blocks (PRBs), asingle PRB of the set of PRBs comprising a number of frequencysub-carriers over a Transmission Time Interval (TTI), using anaggregation level of L Control Channel Elements (CCEs) in one of M^((L))candidate PDCCH locations, the apparatus comprising: a comparatorconfigured to determine whether the number of REs in a PRB available fortransmitting PDCCHs is smaller than a predetermined number; a searcherconfigured to determine a first number of M^((L)) candidate PDCCHlocations if the number of REs in a PRB available for transmittingPDCCHs is smaller than the predetermined number or to determine a secondnumber of M^((L)) candidate PDCCH locations if the number of REs in aPRB available for transmitting PDCCHs is larger than or equal to thepredetermined number wherein the first number is different than thesecond number; and a decoder configured to decode PDCCHs in therespective candidate PDCCH locations.
 26. The apparatus of claim 25,wherein the predetermined number of REs in a PRB is determined so thatthe transmission of a Downlink Control Information (DCI) format in aPDCCH transmitted using one CCE is with a predetermined code rate. 27.The apparatus of claim 25, wherein for L=1, the first number of M^((L))candidate PDCCH locations is zero and the second number of M^((L))candidate PDCCH locations is larger than zero.
 28. The apparatus ofclaim 27, wherein for at least one value L>1, the first number ofM^((L)) candidate PDCCH locations is larger than the second number ofM^((L)) candidate PDCCH locations.
 29. The apparatus of claim 25,wherein the apparatus determines the number of REs in a PRB availablefor transmitting PDCCHs in the TTI from the total number of REs in a PRBafter excluding at least REs used to transmit Common Reference Signals(CRS), Channel State Information Reference Signals (CSI-RS), and othercontrol channels.
 30. The apparatus of claim 25, wherein the basestation transmits PDCCH in one of two sets of PRBs configured to theapparatus for PDCCH transmissions through higher layer signaling. 31.The apparatus of claim 30, wherein the number of PRBs in the first setof PRBs is larger than the number of PRBs in the second set of PRBs. 32.The apparatus of claim 31, wherein for at least one value of L, thenumber of PDCCH decoding operations in the first set of PRBs isdifferent than in the second set of PRBs.
 33. The apparatus of claim 25,wherein the number of CCEs in a PRB is two if the number of REs in a PRBavailable for transmitting PDCCHs is smaller than the predeterminednumber, and the number of CCEs in a PRB is four otherwise.
 34. Theapparatus of claim 25, wherein the number of CCEs in a PRB is alwaysfour.